The tempering hardness (H) of steel depends on the tempering temperature (T) and tempering time (t), and there is a certain functional relationship between the three, i.e., H = f (T, t). When t is a fixed value, the functional relationship between H and T can be divided into four types: (1) linear (2) parabolic type. (3) power function type. (4) linear and power function of the composite type. Because of the latter two types in use, calculation and graphing is extremely inconvenient, so in most cases, it will be simplified to linear and parabolic type, using the empirical equation can be expressed as follows: H = a1 + k1 T H = a2 + k2 T where a1, a2, k1, k2 are specific coefficients. Based on the data from actual process tests and relevant references, the tempering equations for some commonly used steel grades are calculated and corrected using mathematical and statistical methods. Practice has proved that these empirical equations have important applicable value. Steel No. Quenching temperature / quenching medium Tempering equation 45 840 / water H = 62 – (1/9000) T 2 20Cr 890/Oil H = 50 – (2/45)T 38CrMoAl 930/oil H = 64 – (1/25)T (T<550) H = 95 -(1/10)T (T>550) 40Cr 850/oil H = 75 -(3/40)T 50CrVA 850/oil H = 73 -(1/14)T 60Si2Mn 860/oil H = 68 – (1/11250)T 2 65Mn 820/oil H = 74 -(3/40)T T8 800/water H = 78-(7/80)T T10 780/water H = 82.7 – (1/11) T CrWMn 830/oil H = 69 – (1/25) T Cr12 980/oil H = 64 – (1/80)T (T<500) H = 107.5 -(1/10)T (T>500) Cr12MoV 1000/oil H = 65 – (1/100) T(T<500) 9CrSi 865/oil H = 69 -(1/30)T 5CrNiMo 855/oil H = 72.5 -(1/16)T 5CrMnMo 855/oil H = 69 -(3/50)T W18Cr4V 1280/oil H = 93 -(3/31250)T 2 GCr15 850/oil H = 733 – (2/3)T Instructions for use. (1) require the chemical composition and mechanical properties of raw materials in line with national technical standards (GB, YB, etc.), the maximum outer diameter (or relative thickness) is close to or less than the quenching critical diameter. (2) in the quenching temperature, tempering time for a fixed value of the conditions, tempering equations are only applicable to conventional quenching and tempering process; can not be used for sub-temperature quenching, composite heat treatment, deformation heat treatment and other processes. (3) in the heat treatment process, should also choose the correct quenching medium, so that the cooling capacity to meet the process requirements; steel as required for preparatory heat treatment. (4) taking into account the impact of random factors, steel heat treatment, tempering the actual hardness and temperature and the number of calculated allow a 5% error.

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