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宮城県に在住する刀匠・九代法華三郎信房氏とご子息の栄喜氏のご協力により，代々継承している作刀技術のうち，「卸し鉄」「折り返し鍛錬」「焼き入れ」の３つについて，自然科学的な観点から調査を行い，下記の諸点が明らかになった。卸し鉄では，同じ炉を使い，ほとんど同じような動作をしているのに，軟鉄への浸炭と銑鉄からの脱炭という正反対の反応を起こすことができる。両者において，炉内ではまったく異なるメカニズムが働いていると推測される。すなわち，軟鉄の浸炭では，炉の上部で固体の鉄に炭素が吸収され，融点が下がって半溶融状態となり，炉底に垂れ落ちていく。炉底ではできるだけ風があたらないようにして，脱炭が起こらないようにする。一方，銑鉄の脱炭では，炉の上部で鉄が溶解して液体状態になり，炉底に少しずつ流れ落ちていく。炉底では羽口からの風があたるようにして，鉄中の炭素を燃焼させ，炭素濃度を下げる。折り返し鍛錬において，折り返し回数が増えるにつれて，炭素濃度の均一化されていく様子が観察された。参考文献などにある「折り返し鍛錬によって介在物が減少していく」という現象は確認されず，鍛接面に生じるものもスラグに由来するものも，折り返し回数が増えるほど小さくなり均一に分散されていくことがわかった。鍛造開始時の加熱温度については，仮着けでも泥沸かしでも，鉄の炭素濃度に応じて異なる傾向がみられた。また仮着けと泥沸かしの工程では，加熱温度，作業を行う温度，作業継続時間に相違がみられた。これはそれぞれの工程での目的と刀匠の意識が反映されているものと考えられた。焼き入れにおいて，沸と匂を作りわける場合の加熱温度の違いを実験的に確認できた。これは刀匠の感覚とも整合的であった。また焼刃土の下の鉄の温度の測定により，焼刃土が地部の徐冷に役立っていることが確認された。, We carried out scientific research on three traditional techniques, oroshi-gane, orikaeshi-tanren and yaki-ire, inherited by the swordsmiths, HOKKE-Saburo Nobufusa 9th and his son, HOKKE-Eiki, in Miyagi prefecture. The results are as follows;1. With oroshi-gane technique, adjustment of carbon contents in steel, they can both carburize iron and decarburize cast iron in a same furnace. In each process the different mechanisms are assumed to work in the furnace. In the case of carburizing of iron, solid iron absorb carbon at the upper part of the furnace and it stickily drop down in semi-melted. The wind through tuyere hardly blow in the product at the bottom of the furnace, On the contrary, in the case of decarburizing of cast iron, cast iron melt at the upper and the molten material drip down. It is decarburized at the bottom of the furnace by the wind through tuyere.2. With orikaeshi-tanren technique, duplicated folding and hammer welding, the carbon content is homogenized in increasing of times of folding. Each inclusion is made smaller and is dispersed uniformly in increasing of times of folding. The temperature of forging is different according to the concentration of carbon in raw material.3. In yaki-ire technique, quenching, the heating temperature of the nie and nioi, the quenching patterns at the blade, is measured. The temperature of the steel under coating clay is also measured at some intermediate period in quenching process, and it is confirmed that the coating clay have an effect on relatively slow cooing of the ground part.

大鍛冶は，前近代の砂鉄を原料とする製鉄法において，銑鉄を脱炭して軟鉄を作る精錬方法として，近世から明治時代まで行われていた技術である。考古学的な遺跡の発掘調査は行われているが，現在は技術の伝承が途絶えているため，作業内容の詳細は二編の論文からしか推測できなかった。われわれは大鍛冶を再現するために，実験炉を構築して様々な条件で操業を行い，技術の詳細と炉内反応の実態について考察を行った。その結果，現代のたたら吹き製鉄によって作られた銑を原料として，小規模ながら大鍛冶を再現することに成功した。基本的な反応機構は以下の通りであると推測される。1．はじめに，原料銑鉄の表層部に脱炭層が形成されない800℃程度を目標として予備加熱を行なう。全体の温度が上がったところで，内壁が反応の始まる温度（1150℃前後）になるまで速やかに温度を上げる。2．羽口からの風によって，アーチ状に組まれた原料銑鉄の下部にある空間の気圧が低くなると，原料と炉内壁の羽口側の隙間から空気とともに一酸化炭素が吸い込まれる。これらが原料下部空間を通過する際に燃焼し，内壁が加熱される。3．溶融した銑鉄が炉底に落ち，そこに羽口からの風があたることによって，ある程度時間をかけて脱炭が進行する。したがって，溶融が一度に行われてしまうと内部まで十分な脱炭が行われず，流銑の状態になってしまう。溶融銑鉄がわずかずつ垂れ落ちて脱炭する，というプロセスが連続的に達成されるような内壁温度を維持するためには，反応状況をみて送風量を微調整することが必要である。, O-kaji was a process of refining to decarburize pig iron to low-carbon iron during Yedo to Meiji periods in Japanese traditional iron manufacturing by using iron sand as raw material. Though archaeological excavations were conducted on O-kaji sites, the accession of the process had end and the technical detail was recorded in only two research papers.We constructed experimental furnaces of o-kaji and operated them under various conditions to prospect the details of the technology and situation of the reaction in the furnace. As the result, we succeeded at reappearance of O-kaji, even in a smaller-scale, by using pig iron made with the modern tatara-smelting process operated by The Society for Preservation of Japanese Art Swords.We supposed the basic reaction mechanism of o-kaji as follows;1. The temperature of preheating was about 800℃ , at which decarburized layer was not produced at the surface. After the whole material pig iron was heated enough, the temperature was rapidly risen to around 1150℃ , at which the inside-wall of pig iron started to melt.2. With the wind from tuyere, the air pressure under the arch-like pig iron reduced. Then carbon monoxide was drawn into there with air from gap between the pig-iron and the furnace wall. They burned under the empty space under the pig-iron and heated the inside-wall.3. Decarburizing was processed with taking a certain amount of time at the bottom of furnace with being blown by the wind from furnace after melted pig iron dripped. So the melting should proceed in small steps otherwise decarburizing did not make progress inside of the massive melted pig iron. Fine control should be needed to keep the adequate temperature of inside-wall for successive process of little by little melting, drip and decarburizing.

Usual heat treatments of steels like austenitization are generally conducted in air. In such atmosphere, a part of the atoms of carbon could be removed from the superficial zone of steel. Indeed, those atoms of carbon, combined with oxygen present in atmosphere, can take gaseous form of carbon monoxide due to the great attraction between atoms of carbon and oxygen. This well-known phenomenon is called decarburizing. It can change microstructure to a large extent and, as a result, bring dramatic modifications of mechanical properties of steel, like decrease of fatigue lifetime. To characterize the extent of decarburizing phenomenon, observations by optical microscopy and/or hardness profiles measurements must be performed in a cross section, as it is advised by international standard. Until today, the eddy current technique is used to detect superficial defects. In practice, the control consists to create two groups of available samples or not, from a large sampling. In this study, we propose to estimate the decarburizing extent. In the present work, different durations of austenitizing at 920 °C temperature before oil quenching (50 °C) were performed on the SAE 92V45 steel in order to obtain various morphologies and different total depths of the decarburized zone. We will show, in the continuation, how eddy currents control is used to assess the level of decarburizing after a Fourier transformation performed on the output signal. This analysis allows us to link the harmonic decomposition of the signal to the duration of the heat treatment and/or to the total decarburizing depth and, consequently, to the mechanical properties.

In the present study, gears made of 21NiCrMo2 (AISI 8620) steel were subjected to heat treatments including carburizing, decarburizing, boriding and hardening. Carburizing, decarburizing and boriding were performed in a gaseous atmosphere, a salt bath consisting of 60% NaCl and 40% NaCO3, and a liquid medium containing borax and silicon carbide, respectively. Borocarburazing was carried out in two steps: carburizing and then boriding. Some specimens were treated to obtain different carbon concentrations and to observe the effect of carbon content on the boriding process. This process, consisting of carburizing followed by decarburizing and finally boriding, is named borodecarburizing. The microstructures and phase compositions of the diffusion layers were examined by means of X-ray diffractometry, scanning electron microscopy and optical microscopy. The microhardness profiles of these layers were studied by a Vickers indenter. The hardness value obtained by the borodecarburizing process is 10% higher than a borocarburized specimen's hardness. One-phase iron boride zone (Fe2B) was observed in the layers. This phase is preferred due to its mechanical properties.

In the present study, gears made of 21NiCrMo2 (AISI 8620) steel were subjected to heat treatments including carburizing, decarburizing, boriding and hardening. Carburizing, decarburizing and boriding were performed in a gaseous atmosphere, a salt bath consisting of 60% NaCl and 40% NaCO3, and a liquid medium containing borax and silicon carbide, respectively. Borocarburazing was carried out in two steps: carburizing and then boriding. Some specimens were treated to obtain different carbon concentrations and to observe the effect of carbon content on the boriding process. This process, consisting of carburizing followed by decarburizing and finally boriding, is named borodecarburizing. The microstructures and phase compositions of the diffusion layers were examined by means of X-ray diffractometry, scanning electron microscopy and optical microscopy. The microhardness profiles of these layers were studied by a Vickers indenter. The hardness value obtained by the borodecarburizing process is 10% higher than a borocarburized specimen’s hardness. One-phase iron boride zone (Fe2B) was observed in the layers. This phase is preferred due to its mechanical properties.

It was proposed to solve urgent problems of saving scarce and costly high-alloyed and wear resistant steel grades (containing Ni, Mo, V, W, Nb) and increasing wear resistance of metal parts by means of creating surface modifications of metastable phase-structural complexes in inexpensive economical alloys of the similar structural classes. The objective of this work is to investigate the influence of alloying elements upon the formation of the structure, metastability of austenite and properties of chromium-manganese steel grades, undergoing carburizing and manganese steel undergoing decarburizing. In this work the new ways and processes of surface modifications of metastable phase-structural states were developed:- carburizing Fe-Cr-Mn steels with various contents 2…22 % Cr with subsequent quenching at optimal temperatures of austenitization;- decarburizing austenitization for a specified depth of high-alloyed wear resistant steel grades (110Mn13 – Hadfield steel, 130Cr12Mo etc.) causing destabilization of austenite and realization deformation induced martensite γ→α′ transformation in the process of wear, Предложено решение актуальных проблем экономии дефицитных и дорогостоящих высоколегированных и износостойких марок стали (содержащих Ni, Mo, V, W, Nb) и повышение износостойкости металлических деталей путем создания поверхностных модификаций метастабильных фазово-структурных комплексов в недорогих экономичных сплавах подобных структурных классов. Целью данной работы является исследование влияния легирующих элементов на формирование структуры, метастабильность аустенита и свойств хромо-марганцевых марок стали после цементации и мар-ганцевой стали после обезуглероживания. В этой работе были разработаны новые способы и процессы поверхностных модификаций метастабильных фазово-структурных состояний:- цементация Fe-Cr- Mn сталей с различным содержанием 2 ... 22 % Cr с последующей закалкой при оптимальных температурах аустенитизации; - обезуглероживающая аустенитизация на определенную глубину высоколегированных износостойких сталей (110Г13 – сталь Гадфильда, 130Х12M и т.д.) вызывающая дестабилизацию аустенита и реализацию деформационного мартенситного γ → α ' превращения в процессе изнашивания, Запропоновано вирішення актуальних проблем економії дефіцитних і дорогих високолегованих і зносостійких марок сталі (вміщаючих Ni, Mo, V, W, Nb та ін.) та підвищення зносостійкості металевих деталей шляхом створення поверхневих модифікацій метастабільних фазово-структурних комплексів в недорогих економічних сплавах подібних структурних класів. Метою даної роботи є дослідження впливу легуючих елементів на формування структури, метастабильність аустеніту і властивостей хромо-марганцевих марок сталі після цементації і марганцевої сталі після зневуглецювання. У цій роботі були розроблені нові способи і процеси поверхневих модифікацій метастабільних фазово-структурних станів: - цементація Fe - Cr- Mn сталей з різним вмістом 2 ... 22 % Cr з наступним загартуванням при оптимальних температурах аустенітізації; - зневуглецювання аустениту на певну глибину високолегованих зносостійких сталей (110Г13 - сталь Гадфільда, 130Х12M і т.д.), що призводить до дестабілізації аустеніту і реалізації деформацій мартенситних γ → α ' перетворень в процесізносу

Carbon is the most important element going in the steels composition since it largely contributes to their mechanical performance. During the heat treatment of steels, a part of atoms of carbon could be removed from the superficial zone of the steel, which is the result of the atmospheric oxygen attraction by forming gaseous carbon monoxide. This phenomenon, called decarburizing, can change microstructure in a large extent and, as a result, mechanical properties of the steel. This could lead to unsuitable properties for the service life of mechanical parts. In order to prevent such part from breaking in service, it is necessary to know the affected zone by the decarburizing process. For this purpose, the most used technique is a visual observation by optical microscopy of a cross section of the material. This technique is often associated to the hardness profile obtained by Vickers or Knoop indentations in the same section. Depending on the material and on the specimen preparation, some discrepancies are often observed between the two informations. On the other hand, these techniques require a long preparation and cautious interpretation. Then we propose here to use eddy current testing, which is widely employed to detect fatigue cracks, to give some information about changes in microstructure and to examine carburizing of steel from both mechanical and microstructural point of view. For carburizing, eddy current has been successfully connected to the increase of micro-hardness near the surface. This last result has particularly motivated us to use eddy current to analyze decarburizing. In the present work, different durations in the furnace at a temperature of 920°C before oil quenching were performed on 54SiCrV6 (SAE 92V45) steel in order to obtain various morphologies of the decarburized zone. We show that eddy current test may be used to qualify the level of decarburizing since, after a convenient Fourier transformation, three components of the amplitude of the signal are directly linked to the duration of the heat treatment. Associated to optical and hardness measurements, it is also shown that the eddy current signal is well related to the decarburizing depth.