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Metallurgy and Materials Engineering Department University of Indonesia Semester Ganjil 2013/2014 High Strength Low Alloy (HSLA) Prof. Dr.-Ing. Bambang Suharno Kuliah Baja Paduan dan Paduan Super University of Indonesia Metallurgy and Materials Engineering Department UI University of Indonesia Metallurgy and Materials Engineering Department UI Diagram Fe-Fe3C 0.5% C ferrite + pearlite 1.5% C ferrite + cementite University of Indonesia Metallurgy and Materials Engineering Department UI HSLA They have a carbon content between 0.05–0.25% to retain formability and weldability. Other alloying elements include up to 2.0% manganese and small quantities of copper, nickel, niobium, nitrogen, vanadium, chromium, molybdenum, titanium, University of Indonesia Metallurgy and Materials Engineering Department UI CONTRIBUTIONS TO STRENGTH IN STEELS Base material Solid solution strengthening (i.e., %Mn) Grain size (ferrite) Precipitates (distance between ppts) Cold work (dislocation density) Hardening (Martensite) University of Indonesia Metallurgy and Materials Engineering Department UI STRENGTHENING LOW C STEELS (0-0.3%C) 2 major ways: increase carbon content – sacrifice % elongation; toughness because of Fe3C decrease grain size – increase strength but doesn’t affect ductility – Hall-Petch Equation => better strength without sacrificing ductility and toughness trend: use fine grained steels and lower C content University of Indonesia Metallurgy and Materials Engineering Department UI ASTM GRAIN SIZE University of Indonesia Metallurgy and Materials Engineering Department UI University of Indonesia Metallurgy and Materials Engineering Department UI GRAIN SIZE AND STRENGTH University of Indonesia Metallurgy and Materials Engineering Department UI ASTM GRAIN SIZE Grain boundaries act as barriers to dislocation motion Dislocation have a hard time crossing grain boundary. If the grains are smaller, there would be more grains and grain boundary. This would impeded the dislocation. University of Indonesia Metallurgy and Materials Engineering Department UI EFFECT OF GRAIN SIZE ON STRENGTH University of Indonesia Metallurgy and Materials Engineering Department UI APPLICATIONS University of Indonesia Metallurgy and Materials Engineering Department UI High Strength Low Alloy (HSLA) steels Traditionally for highest strength in a structural steel the C & Mn levels would be increased i.e. 0.25 - 0.30 %C & 1.2 - 1.5 %Mn An increase of 1% Mn will increase YS by ~14% This led to problems with: – Weldability (problem with increased C and Mn) – Brittle failure (problem with increased C) New approach required: strength but C Now have steels with YS to 550 MPa but with excellent weldability and brittle fracture resistance University of Indonesia Metallurgy and Materials Engineering Department UI High Strength Low Alloy (HSLA) steels Solid solution hardening (Mn) Decrease ferrite grain size by Controlled rolling Controlled cooling Precipitation hardening Nb (C,N) VC Typical x70 pipeline steel %C = 0.06; %Mn = 1.50; %Nb and/or V ~0.04 Controlled rolling to produce very fine grain size University of Indonesia Metallurgy and Materials Engineering Department UI CONTROLLED ROLLING SCHEMATIC University of Indonesia Metallurgy and Materials Engineering Department UI Strength in HSLA steels + Standard C-Mn Steel 200-300 MPa + Decrease grain size 100-134 MPa + Increase Mn 67 MPa + Increase Nb,V,Ti ppt hardening 67-100 MPa Total: 434-600 MPa Can now afford to lower the C content and still have 470-500 MPa steel Can have any strength level wanted by varying the degree of strengthening components University of Indonesia Metallurgy and Materials Engineering Department UI Some Specifications applicable to Steel Products and other Metals University of Indonesia Metallurgy and Materials Engineering Department UI The Most Widely Used System for Designating Steels SAE-AISI University of Indonesia Metallurgy and Materials Engineering Department UI Carbon and Alloy Steel Applications University of Indonesia Metallurgy and Materials Engineering Department UI Mechanical Properties of Carbon and Alloy Steels University of Indonesia Metallurgy and Materials Engineering Department UI Effect of alloying elements on TTT curves (Mo-Steel) Medium C steel – 1040 (0.4%C + 1%Mn) – 5140 (0.4%C + 1%Mn + 0.9%Cr) – 4140 (0.4%C + 1%Mn + 1.0%Cr + 0.2%Mo) – 4340 (0.4%C + 1%Mn + 0.8%Cr + 0.3%Mo + 1.85Ni) University of Indonesia Metallurgy and Materials Engineering Department UI TTT curve – 1040 (C + Mn) University of Indonesia Metallurgy and Materials Engineering Department UI TTT curve – 5140 (C+Mn+Cr) University of Indonesia Metallurgy and Materials Engineering Department UI TTT curve – 4140 (C+Mn+Cr+Mo) University of Indonesia Metallurgy and Materials Engineering Department UI TTT curve – 4340 (C+Mn+Cr+ Ni+Mo) University of Indonesia Metallurgy and Materials Engineering Department UI TTT Curves (1040, 5140, 4140, 4340) With increased alloys, P+B noses shift right i.e. hardenability increases Plain C steels can’t be hardened to form martensite except at very high cooling rates i.e. small section sizes University of Indonesia Metallurgy and Materials Engineering Department UI University of Indonesia Metallurgy and Materials Engineering Department UI
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