For medium-alloy steels up to 6308C (11668F), with a cooling rate of 15–20 K/h (furnace cooling) For high-alloy steels up to 6008C(11128F), with a cooling rate of 10–15 K/h (furnace cooling) Further cooling below the temperatures indicated is usually performed in air 6.2.5 RECRYSTALLIZATION ANNEALING Recrystallization annealing is an annealing process at temperatures above the recrystalliza- tion temperature of the cold-worked material, without phase transformation, that aims at regeneration of properties and changes in the structure that exists after a cold-forming process 600ЊC 130 110 90 70 0 50 100 150 200 Time, h Hardness, HRB 625ЊC 650ЊC 675ЊC 700ЊC FIGURE 6.78 Hardness of an unalloyed steel with 0.89% C after soft annealing, depending on the spheroidization time and temperature. (From H.J. Eckstein (Ed.), Technologie der Wa ¨ rmebehandlung von Stahl, 2nd ed., VEB Deutscher Verlag fu ¨ r Grundstoffindustrie, Leipzig, 1987.) a b 200 Turning speed (v 60 ), m/min Tensile strength R m , N/mm 2 150 100 50 500 600 700 900800 1000 c FIGURE 6.79 Influence of the ultimate tensile strength and degree of spheroidization on machinability of steels for carburizing and structural steels for hardening and tempering, expressed as 1 h turning speed (v 60 ) in m/min. (a) Spheroidization degree less than 30%; (b) spheroidization degree between 40 and 60%; (c) spheroidization degree greater than 70%. (From G. Spur and T. Sto ¨ ferle (Eds.), Handbuch der Fertigungstechnik, Vol. 4/2, Wa ¨ rmebehandeln, Carl Hanser, Munich, 1987.) ß 2006 by Taylor & Francis Group, LLC. For medium-alloy steels up to 6308C (11668F), with a cooling rate of 15–20 K/h (furnace cooling) For high-alloy steels up to 6008C(11128F), with a cooling rate of 10–15 K/h (furnace cooling) Further cooling below the temperatures indicated is usually performed in air 6.2.5 RECRYSTALLIZATION ANNEALING Recrystallization annealing is an annealing process at temperatures above the recrystalliza- tion temperature of the cold-worked material, without phase transformation, that aims at regeneration of properties and changes in the structure that exists after a cold-forming process 600ЊC 130 110 90 70 0 50 100 150 200 Time, h Hardness, HRB 625ЊC 650ЊC 675ЊC 700ЊC FIGURE 6.78 Hardness of an unalloyed steel with 0.89% C after soft annealing, depending on the spheroidization time and temperature. (From H.J. Eckstein (Ed.), Technologie der Wa ¨ rmebehandlung von Stahl, 2nd ed., VEB Deutscher Verlag fu ¨ r Grundstoffindustrie, Leipzig, 1987.) a b 200 Turning speed (v 60 ), m/min Tensile strength R m , N/mm 2 150 100 50 500 600 700 900800 1000 c FIGURE 6.79 Influence of the ultimate tensile strength and degree of spheroidization on machinability of steels for carburizing and structural steels for hardening and tempering, expressed as 1 h turning speed (v 60 ) in m/min. (a) Spheroidization degree less than 30%; (b) spheroidization degree between 40 and 60%; (c) spheroidization degree greater than 70%. (From G. Spur and T. Sto ¨ ferle (Eds.), Handbuch der Fertigungstechnik, Vol. 4/2, Wa ¨ rmebehandeln, Carl Hanser, Munich, 1987.) ß 2006 by Taylor & Francis Group, LLC. 100 0 (a) Temperature, 8C 200 300 400 500 600 700 800 900 0.01 0.1 1 Time, s 10 100 1000 100 0 (b) Temperature, ЊC 200 300 400 500 600 700 800 900 0.01 0.1 1 Time, s 10 100 1000 FIGURE 6.117 Comparison of measured (- - -) and calculated (—) cooling curves for the center of a 50-mm diameter bar quenched in (a) mineral oil at 208C, without agitation and (b) 25% PAG polymer solution, 408C bath temperature, and 0.8 m/s agitation rate. 1 0 100 200 300 400 500 600 700 800 900 1000 AISI 4140 Chemical composition Austenitizing temp. 850 ЊC Time, s 10 Temperature, ЊC 10 2 10 3 10 4 10 5 10 6 C 0.38 0.23 0.64 0.019 0.013 0.99 0.17 0.16 0.08 <0.01 Si Mn P S Cr Cu Mo Ni V 58 2 3 85 75 B A M M s S 3/4 R 2 7 30 70 60 40 60 40 A c3 A c1 F P C 10 5 12 75 53 52 34 28 27 230 220 200 FIGURE 6.118 CCT diagram of AISI 4140 steel with superimposed calculated cooling curves for surface (S), three-quarter radius (3/4R) and center (C) of a round bar of 50-mm diameter. ß 2006 by Taylor & Francis Group, LLC. ASTM 3 100 50 20 0 −50 −100 −150 200 400 600 800 Yield strength R p, N/mm 2 Transition temperature, ЊC 1000 1200 1400 RT ASTM 7 ISO-V longitudinal 100% F + P 50% F + P/50% B 30% F/70% B 10% F/90% B 100% B u 100% B l 25% M/75% B 50% M/50% B 75% M/25% B GS GS GS F−P B M FIGURE 6.133 Transition temperature as a function of yield strength and microstructure. F, Ferrite; P, pearlite; B, bainite; B u , upper bainite; B 1 , lower bainite; M, martensite; GS, grain size (ASTM). (From G. Spur and T. Sto ¨ ferle (Eds.), Handbuch der Fertigungstechnik, Vol. 4/2, Wa ¨ rmebehandeln, Carl Hanser, Munich, 1987.) M M (a) (b) (c) 25 20 15 70 50 60 40 30 20 10 0 250 200 150 100 50 0 300 500 700 Yield strength R p , N/mm 2 900 1100 1300 10 5 Elongation, % Contraction Z, % 0 B B F + P F + P M B F + P Impact energy (20ЊC) FIGURE 6.134 (a) Elongation; (b) reduction of area; and (c) impact toughness of hardened and tempered steels having about 0.4% C, as a function of structure constituents and yield strength. F, Ferrite; P, pearlite; B, bainite; M, martensite. Grain size: ASTM 6–7. Impact toughness: ISO notch specimens. Testing direction: longitudinal. (From G. Spur and T. Sto ¨ ferle (Eds.), Handbuch der Ferti- gungstechnik, Vol. 4/2, Wa ¨ rmebehandeln, Carl Hanser, Munich, 1987.) ß 2006 by Taylor & Francis Group, LLC. . 1000 c FIGURE 6 .79 Influence of the ultimate tensile strength and degree of spheroidization on machinability of steels for carburizing and structural steels for hardening and tempering, expressed as. ultimate tensile strength and degree of spheroidization on machinability of steels for carburizing and structural steels for hardening and tempering, expressed as 1 h turning speed (v 60 ) in m/min Wa ¨ rmebehandlung von Stahl, 2nd ed. , VEB Deutscher Verlag fu ¨ r Grundstoffindustrie, Leipzig, 19 87. ) a b 200 Turning speed (v 60 ), m/min Tensile strength R m , N/mm 2 150 100 50 500 600 70 0 900800