Keywords: steel, hardenability, Steel, chemical composition, quenching temperature, eating temperature, characteristics of the cooling medium, ways of cooling, means of cooling, shape,

　　The main factors affecting the hardenability of steel are; the chemical composition of steel, quenching and heating temperature, the characteristics of the cooling medium, the way and method of cooling, the shape and size of the part and the heating method.

(I) the chemical composition of steel is one of the most important factors affecting the hardenability. Where in the steel to cause ‘c’ curve right or left shift of the alloying elements, have a great impact on the hardenability. Make ‘c’ curve right element will improve the hardenability of steel; make ‘c’ curve left element will reduce the hardenability of steel. Such as 45 steel and 40Cr steel, its carbon content is almost the same, but, as the former does not contain chromium, the latter contains chromium elements about 1 per cent, in the same heat treatment conditions, their hardenability is obviously different, 45 steel can only be quenched far from 3.5-9.5 mm, while the 40Cr steel can be quenched through 25-32 mm.

(2) heat treatment cooling medium cooling characteristics and cooling rate, the steel hardenability also has a great impact. Cooling speed fast, hardenability is improved, cooling speed but, hardenability is reduced. For example, 45 steel cooling in water and cooling in oil, its hardenability is different, cooling in water, can be quenched 11 a 20 mm, cooling in oil, can be quenched 3.5-9.5 mm.

(3) the shape and size of the parts, heating temperature, cooling, etc., to varying degrees, are affecting the hardenability of steel. Small shape size, high heating temperature, continuous cooling, etc. can improve the hardenability to a certain extent; while the shape size, low heating temperature, isothermal cooling, etc. can make the hardenability decline.

(4) the way of heating will also affect the hardenability, in practice this is very important, we are often easy to ignore this point. Because the heating method is different, the heating effect is different. For example, with a box-type electric furnace than salt bath furnace oxidation, decarburisation phenomenon is serious, it will reduce the hardenability.

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