MatSE 259 Exam 2 Review Session Exam structure – same as Exam 1 Please write your student I.D. on the answer sheet Please mark your answers clearly Do not leave a question unanswered – there is no negative marking Hand in both question and answer sheets at the end of the exam – the questions will be posted on the website on Thursday after the last conflict exam

Diffusion Requirements: Empty adjacent site Sufficient energy Types: Interdiffusion or Impurity diffusion and Self diffusion Vacancy diffusion and Interstitial diffusion Steady-state diffusion: Fick’s first law

Solid Solutions A solid solution consists of at least two different atoms: solute and solvent. The crystal structure of the solid solution is that of the solvent, and the solute atoms occupy either interstitial or substitutional positions. Solubility limit depends upon: Atomic Size Crystal Structure Electronegativity Valences

Fe-C (Fe-Fe3C) Phase Diagram A phase diagram (equilibrium/constitutional diagram) shows the relationship between temperature and the composition and quantities of the phases of a system. The (Fe-Fe3C) phase diagram tells you: The phases present The composition of the phases present The fractions (mass or volume) of the phases present Eutectoid Reaction: Hypo-eutectoid steels give pro-eutectoid a and pearlite Hyper-eutectoid steels give pro-eutectoid CM and pearlite

Fe-C (Fe-Fe3C) Phase Diagram (contd.) Textbook Example 9.65 HYPOEUTECTOID U V T HYPEREUTECTOID U V

Martensite (MAR) Transforms from AUS on quenching or rapid cooling via a diffusionless shear process (CCP BCT) Very hard and strong Hardenability of a steel: ability to make MAR (depth of transformation to martensite) Controlling the position of T-T-T plots: - Changing C content - Alloying - Increasing AUS grain size MAR tempering produces tempered martensite; the mstructure of which consists of extremely small and uniformly dispersed cementite particles in a continuous ferrite matrix. Tempered Martensite is a lot tougher than MAR, depending on the tempering temperature.

T-T-T curves Textbook Example 10.15 (a) (b) (c) Ms Mf

T-T-T Curves Textbook Example 10.18 (d) (a) (c) (b)

Stainless Steels (Cr > 11% wt) Based on the predominant mconstituent, S.S. are classified as: 1. Martensitic (heat treatable) Medium Cr, Low Ni, Medium-High C 2. Ferritic (not heat treatable) Medium Cr, Low Ni, Medium C a ferrite is the predominant phase 3. Austenitic (not heat treatable) High Cr, High Ni, Low C g phase extended to room temperature